William Hague's special adviser has resigned over "untrue and malicious" allegations made against him, the Foreign Secretary has said.
Mr Hague said suggestions Christopher Myers' appointment was due to an improper relationship between them were "utterly false".
In a statement, he also denied his marriage to wife Ffion was in trouble.
He revealed they have suffered multiple miscarriages and are still grieving the loss of a pregnancy this summer.
Mr Myers, 25, was employed by Mr Hague during the election campaign as a constituency aide and after the election worked for the foreign secretary as a policy adviser.
Mr Hague's statement, which was issued in his personal capacity and not as foreign secretary, followed speculation in the media and on the internet over the pair's relationship.
BBC deputy political editor James Landale said the statement was "extraordinary", in its detailed response to the allegations and in the revelations about his marriage.
Mr Hague said the story seemed to stem from the fact they "occasionally" shared hotel rooms during the election.
But the MP for Richmond added: "Neither of us would have done so if we had thought that it in any way meant or implied something else.
"In hindsight I should have given greater consideration to what might have been made of that, but this is in itself no justification for allegations of this kind, which are untrue and deeply distressing to me, to Ffion and to Christopher."
Mr Hague, 49, said Mr Myers had "demonstrated commitment and political talent" over the past 18 months and was "easily qualified" for the job he held.
But he said: "He has now told me that, as a result of the pressure on his family from the untrue and malicious allegations made about him, he does not wish to continue in his position. It is a pity that a talented individual should feel that he needs to leave his job in this way."
The foreign secretary then said he felt he had to provide background information to his marriage to Ffion in a bid to stop the "hurtful speculation" about them.
He said: "I have made no secret of the fact that Ffion and I would love to start a family.
"For many years this has been our goal. Sadly this has proved more difficult for us than for most couples.
"We have encountered many difficulties and suffered multiple miscarriages, and indeed are still grieving for the loss of a pregnancy this summer.
"We are aware that the stress of infertility can often strain a marriage, but in our case, thankfully, it has only brought us closer together.
"It has been an immensely traumatic and painful experience but our marriage is strong and we will face whatever the future brings together."
Mr Hague also said several years ago a Sunday newspaper reported that Ffion was three months pregnant without checking the story.
The revelation was made "even more difficult" as the couple "had only just experienced another disappointment", Mr Hague said.
He added: "We have never made this information public because of the distress it would cause to our families and would not do so now were it not for the untrue rumours circulating which repeatedly call our marriage into question. We wish everyone to know that we are very happily married.
"It is very regrettable to have to make this personal statement, but we have often said to each other 'If only they knew the truth'.
"Well, this is the straightforward truth."
Mr Hague said he would not be commenting further.
Mr Hague's biographer Jo-Anne Nadler said: "I think this has arisen out of a sense of frustration and anger on behalf of Mr and Mrs Hague, and also for his colleague Chris Myers.
"There really have been some very mean-spirited and nasty pieces of innuendo in the regular press as well as the internet over the last few weeks.
"If this has coincided, as this statement says, with the Hagues having unfortunately lost a pregnancy, then it must have been absolutely terrible for them and I very much hope that this now puts an end to all of this rather unpleasant speculation."
Conservative blogger Iain Dale said Mr Hague's statement had been forced by rumours on some political blogs.
He said: "There's absolutely no substance to the rumours at all, somebody has lost their job over it for no good reason, William Hague and his wife have been put through psychological hell because of it and I think some people have got to look at themselves in the mirror and think 'Why did we do this?'."