EURUSD moves lower. GBPUSD moves higher. EURGBP moves lower.
It is all in the math.
While the EURUSD is moving lower, the GBPUSD was moving above the 50% and testing the 200 bar MA on the 5 minute chart below. The price has since reversed lower (see 5 minute chart and joined the EURUSDs move lower, but it still remains higher vs. it's lows while the EURUSD makes new lows.
When two pairs move in opposite directions vs. the USD, the cross is in play. And indeed,the EURGBP is on a move lower. What maybe contributing to the move lower? Fundamentally, there has not been anything that may have warranted the last push lower, but technically, there was a break. Looking at the hourly chart, the price fell below the 38.2% retracement of the move down from the may high to the may low at the 0.7259 level. At the same time, the 200 hour moving average was broken. Earlier today, this same dynamic was tried but failed. The 2nd time was not so fortunate. The next target for the EURGBP is being tested at the 0.7236 level. Below that the 100 hour MA becomes the focus at the 0.72168.
The GBPUSD has since reversed and joined the dollar buying. That may slow the EURGBP decline, but being back below the 200 hour MA and the 38.2% retracement is good news for the bears.