The argument is over a tiara Trixie was planning to wear as her "something old, something borrowed and something blue", but which has been sold by Matthew's mother.
Trixie believes Matthew lied about this, but he says although his mother had sold it, she thought she could get it back as she sold it to a friend. You can watch the full clip here.
In the video, Matthew explains that after his father was first ill, "she wanted to take him on a cruise and the tiara was just languishing there".
Trixie asks why they couldn't have kept the tiara and gone on the cruise but Matthew says: "Perhaps things weren't as liquid as they might have been in their personal accounts".
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He then tells Trixie cuttingly that contrary to what she believes "money doesn't grow on trees", after which she leaves the car and says: "I don't know where you're planning to flounce off but don't you dare follow me in here!"
In spite of this bust-up, fans shouldn't get too worried. In a recent live Q&A with RadioTimes.com’s Abby Robinson, Trixie star Helen George promised that the wedding would be "incredibly romantic".
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George did previously tell RadioTimes.com that there would be some "jeopardy" on the wedding day, with Matthew star Olly Rix adding: "There wouldn't be any drama if it was smooth sailing so buckle up."
The Call the Midwife season finale airs on Sunday 26th February on BBC One at 8pm, while the series is also available to stream on BBC iPlayer. Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to see what's on tonight.
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