Amanda Abbington reportedly quizzed Martin Freeman over a friendship he shared with a showbiz researcher shortly before their split.
Martin Freeman and Amanda Abbington
The 42-year-old actress is understood to have questioned her then-partner about his friendship with the woman and made it clear she was uncomfortable with the situation.
A source said: "Amanda was absolutely furious about it - she confronted him over his relationship with the woman, who works in the business too, and demanded answers.
"She was obviously uncomfortable with how close Martin and this researcher appeared to be - and made her feelings completely clear on the matter. It was very frosty."
Despite this, their split was ultimately "very amicable" and the celebrity duo - who met on the set of the drama 'Men Only' in 2000 - remain good friends.
The source told The Sun newspaper: "In the end Amanda and Martin's split has been very amicable - fortunately they've managed to move on from it and they've both stressed how much they intend to remain the best of friends."
Earlier this month, Martin said that his separation from Amanda is the most "civilised" he's ever heard of.
The 45-year-old actor insisted everything is "cool" between himself and Amanda, who starred alongside him in the BBC adaptation of 'Sherlock'.
He shared: "I mean, we're very friendly and it's all lovely and cool.
"Yes, we've not been together for a while. I mean, we did the series not together. You know enough about me to know that I won't talk about it, but I'm all right, yes. I mean, we're honest to God doing it [separating] in about as civilised a manner as I've ever heard of, you know."
Martin said he will always retain a love for Amanda - with whom he has two children, son Joe and daughter Grace - and he remains a fan of her acting talents.
He explained: "I love Amanda's work. I think she's brilliant as an actor and she's brilliant as a woman and, yes, I love her. I will always love Amanda, but, yes, we're ... you know, that's what's happened. It's just one of those things. It happens, doesn't it? But we're cool."
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